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Gperkins diy sub 2

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21K views 191 replies 10 participants last post by  gperkins_1973 
#1 ·
Hi guys,

I am looking into building another sub but ported this time. That way I can do REW and BFD on them both to see what the actual results would be. My first DIY sealed sub as most of you will be aware was quite a large thing which I used 1" thick mdf. I will be using 0.75" thick mdf this time to bring the weight down a bit. I will either do two single ported 18" subs at 10cu ft each or one dual 18" ported sub. I have attached a winISD file showing the new sub and old sub spl etc.... I have never built a ported sub so this is really new territory for me. I want to tune the ported sub to 10hz and it looks just on the limit on cone excursion so I don't know if that means I won't need a high pass filter or not. It will be running with 2400 watts rms bridged from the Behringer the same as my sealed sub.

It quoting 108db at 10hz and 119db at 20hz for a 20 cu ft box. I have modelled the 20 cu ft so I am guessing that if I take off 6db that will roughly give what a single 10 cu ft would give. Thats about 5db more than my sealed sub at 10 and 20hz. Is that a significant difference.

I guess that the ported sub will be easier to EQ with the BFD with regards to the bottom end. I have put a single 7" port at 116cm long and is quoting the 1st port resonance at 148hz. Not sure if that will be a problem. I haven't done any drawings yet but have a few ideas in mind. If I build one ported sub the dimensions will be 72" long by 24" high by 22" deep and will go between my front speakers under my plasma. Two single ones will be 36" by 24" by 22" and then push together under the plasma. If that didn't work then I could move them into either corner.

Be good to get some advice and thoughts on the above please.

cheers

Graham
 

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#28 ·
Two single ones will be 36" by 24" by 22"
Ok, a 88 cm port won't work as it is 35.5 inches long and the cabinet is 36". Your options are

1. Modify the cabinet dimensions.
2. Use an elbow with the port.
3. Use a hi pass filter and a smaller diameter port.
4. Build one big cabinet for both subs and then the port length is not an issue.
 
#32 ·
Mike is a great help huh?
I'm anxious to see a head to head comparison of the sealed and ported Q18, as you were having problems with the low end.
The ported box tuned to 15hz should solve your problem.
When you get a chance, look up the song The Boogieman - Bass from the Crypt. It can kinda give you a guess at how close in SPL your low bass is to the higher bass. Personally, I find it pretty fun to boost 20hz by 5dB's or so :bigsmile:. Then it really starts to get stuff rattling in my room. I can't keep my closet door shut, which is on the same wall where my sub is. It shakes the door like mad.

Here it is:

 
#33 ·
Sub junkie,

I will check it out. My main issue/worry is that I am pretty flat (playing sine wave test tones) to 15hz and down 4db at 12.5hz but had to boost 20hz by 14db in my first run of graphs. When I looked at my REW measurements they were quite low, so I ran them again changing the spl meter to 70db instead of 80db as I was getting low levels and the graph came out higher hence then only having to boost 20hz by 4db but I reduced 27hz by -12db and 40hz by -10db. I did boost 50hz by 6db as I had a dip.

I have played both clubbed to death and Opus Dei and found no issues at -15db on my onkyo on my preset 3 on my bfd which is boosted by 14db at 20hz. I had the sub trim level on -6db. On the Opus Dei track even on the low frequencies the driver was no where max excursion and I was up to 5 green lights on the input monitor on the BFD. There is defo low frequencies there as the cupboard door was really rattling. I could even play a 5hz sine wave tone and the drivers were moving quite a bit. Didn't register a 1hz though but then I am not surprised.

My sub works out about 10 cu ft without fiberfill and I have added 4kg of that in the box so it should be about 12 cu ft with stuffing. I have learned that unfortunately with the Q subs they need big boxes where as the maelstroms don't. Gutted. That's the learning process for you.

A single ported 10 cu ft sub will give me 110db at 15hz plus room gain which is the same as my dual sealed sub so two single 10 cu ft ported subs would give me about 116db at 15hz without room gain.

Is the extra 6db going to be really noticable when taking in consideration the extra hard work that will go into making two new subs.

I could make two single 10 cu ft sealed subs (effectively 13 cu ft with fiberfill) and that would give each sub a qtc of 0.795 compared to 0.930 that I am getting now. Is there going to be a noticable different in the bottom end between 0.795 and 0.930. Would that mean also I won't need to boost the bottom end like I am at the moment. The dimensions of the single sealed subs would be 42" high by 24" wide by 22" deep with the driver at the bottom on the front.

:help:

cheers

Graham
 
#35 ·
Mike,

I am getting a blu ray player tomorrow so with regards to movies I haven't had too much chance but I have with music and I am more than pleased with music. Low and mid bass is very good indeed. Right here's my problem.

1. Having to boost the bottom end alot as I have my graph flat to almost 10hz. I have tried house curves but I don't like them as it takes too much out of mid bass and my Monitor RS6's don't provide enough of it in my mind. They have a clear sound rather than a bassy sound which is fine.

2. I do play bassy music. Love bassotronics etc... And have to play it loud on occasions.

3. On Opus Dei track there was alot of low end but not enough that it would feel uncomfortable. When playing a song with a very low frequency, should you really feel it or just know its there. Thats was I get but everything really rattles. Way more than the PB13 I had but you knew it was there more on the PB13. Is that down to it being a smaller sub and smaller driver.
As I mentioned at -15db on the onkyo I wanted to go more but I was a bit scared to, to be honest. I had 5 green lights on the BFD and no red ones so I guess I could have gone further. There was quite a bit of excursion but not to its limits.


Would 2 sealed subs with a lower qtc be the better option. That gives an effective 25 cu ft for the two compared to 13 cu ft.

I like the idea of ported as I was thinking it was my only real way to get low low bass but is it.

One more thing, This thing really shakes the plates in the kitchen. You actually feel the force coming through the wall. I had a guy over the other week and he was quite taken back. You actually wonder if the units would fall off.


cheers
Graham
 
#37 ·
When playing a song with a very low frequency, should you really feel it or just know its there. Thats was I get but everything really rattles. Way more than the PB13

Then the sub is obviously outperforming the PB13.

This thing really shakes the plates in the kitchen. You actually feel the force coming through the wall. I had a guy over the other week and he was quite taken back. You actually wonder if the units would fall off.

And you still want more? The sub is good with music, watch a few DVD's and see if the subs performance is good enough and then take it from there.




 
#38 ·
Mike,

I will hire out some blu rays tomorrow and see how they sound. The difficult thing with during the week is my neighbour goes to bed early as she gets up at 4am.

Did you see my graphs by the way.

The other thing, because I have so much output on my sub in the mid to upper bass region is boosting really going to hurt it as I am cutting that by quite a bit.

Here are my BFD filters for preset 3 (most boost)

FR FINE BANDWIDTH GAIN
1 - 20 0 120 14
2 - 25 -2 34 -12
3 - 32 -5 16 -4
4 - 40 -1 10 -12
5 - 50 +2 9 +6
6 - 63 -2 8 -5
7 - 63 -5 28 -1
8 - 80 0 5 -2
9 - 80 10 7 -2

Had to use a few filters as it was a pain to get flat but it worked.


Here

cheers

Gr
 
#41 ·
Sub junkie,

Two Q FI 18's mate in a 10 cu ft box (thats without the stuffing). So I guess with stuffing effectively about 12.5 cu ft. Thats why I thought about building 2 10 cu ft single subs (thats without stuffing). So in theory would mean 25 cu ft for both subs.

cheers

Graham
 
#42 ·
Ive got a question for you mike,

If you are finding it hard to fit your port in the given available space, even when adding a bend, why couldnt you continue the port back over itself, kind of like one tube inside the other and the outer tube acting as a sleeve. You would then need to cap the end of the outer sleeve but I cant see that being too big an issue, and as long as the outer tubes area is twice that of the inner it will maintain a consistent ports size. Doing that would would go a of a long way towards maximizing available space inside the cabinet if its length is causing problems.
 
#44 ·
You can model that in WinISD to get your answer. Thats not how I mean though. I'm still talking about a single port, but one that folds inside itself the maximise space usage. I'll try put up an image of what I mean in a minute

Edit:

Here you go, if this is possible, it would solve the issue of port length being to long in some boxes. Sizes are simple enough to calculate, as are volume displacement. The difficult bit might be bracing the internal port if any issue with it moving occur.
 

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#45 ·
With WinISD if it quotes say a single 8" port of 32" long. You can just make two 8 16" ports. Would that work.
No. Two 8" ports is double the surface area of a single 8" port. You would need to double the length of a single port to achieve the same tuning frequency.

One 8" x 36" port = two 8" x 72" ports.




 
#49 ·
I am very limited on tools as up until my first sub I have never done anything like this before so I don't even own a circular saw. Probably a good thing, wouldn't have any fingers left after about 10 minutes.

I am just using sketchup doing a single 10 cu ft sealed sub in which if I don't decide to go ported build two of them. Will upload soon.

cheers
graham
 
#51 ·
Here's is my first attempt at the single sealed sub side by side the other one. That is one configuration I was thinking about. Or to seperate them and have the drivers at the bottom. Its quite basic at the moment as its taken me ages to figure out sketchup all over again.

There will be another panel going over the top with the wider whole cut out. Just couldn't get it to work right.

These measure 42" wide by 24" high by 24" deep. They are going to be quite big and not out of 1" thick mdf this time.

Not sure if I have enough bracing.

cheers

Graham
 

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#53 · (Edited)
Mike,

I am going to work on a ported sketchup drawing tonight. I was trying to get used to using it again. I would probably use a similar design but have the port coming out of the top. My main problem is having enough room to get a single 7" port 7" away from the edge. A single ported sub would give me the same low end as my dual but obviously 2 ported subs would have 6db more than my dual at 20hz.

The main reason for doing two single sealed subs was to give me a lower qtc but as you say not much more spl. My blu ray didn't turn up yesterday so I am hoping it will today.

Just worked out the single ported sub again and it is just over 11 cu ft and I can use a 90cm 7" port with 1st port resonance at 183hz. What is the lowest port resonance I can get away with without affecting anything.

Will get back with some more drawings.

cheers

Graham
 
#54 ·
Hi guys,

Been thinking again this morning. I have been looking at sub junkies slot ported sub and the dimensions of the sub I had in mind was 42" high by 24" by 24" wide and deep. This will allow me to use a much longer port but am not sure if a slot ported sub is more proned to chuffing compared to a rounded port.

With a port of 20.5" wide by 2.5" high and 111cm long, this gives a first port renosonace of 154hz and a port velocity of 16.5 m/s which is much lower than the round 7" single port that I was looking at the other day. Build wise it looks a little more complicated in the way of needing more tools to cut the angles for the slot port but may be the answer with regards to the sub in mind.

I did think of not bothering after listening to my sealed sub yesterday but I am just curious to find out if it would be better in the low end.

Be good to get people's opinions on slot vs round ports.

cheers

Graham
 
#55 ·
Graham, state the specifics of the modeling you are doing, it saves time have to figure it out. I came up with 9.5 cu.ft tuned to 17 hz with 1000 watts input power and a HPF at 15 hz with one sub.

Round or slot, keep the air speed around 26 m/s and it will be fine. That being said, a slot port 16" x 2" x 23.75" will do the same tuning and you'll gain one cu.ft. net volume for the sub. As a comparison, you would gain 4 - 5 db in the 15 - 30 hz range compared to one sub sealed in 6 cu.ft.
 
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